In recent years, a feed system that performs wireless power feeding (also called wireless power transfer, contact free, or non-contact power feeding) on consumer electronics devices (CE devices) such as, for example, mobile phones and portable music players has attracted attention. In such a feed system, for example, a mobile phone (power receiving unit) is allowed to be charged by placing the mobile phone on a power feeding tray (power feeding unit). Examples of the method of performing such wireless power feeding include an electromagnetic induction method and a magnetic field resonance method (also called magnetic resonance method) utilizing a resonance phenomenon. In these methods, power is transmitted utilizing magnetic coupling between a power feeding coil of a power feeding unit and a power receiving coil of a power receiving unit. Among them, the electromagnetic induction method has an advantage of being able to enhance the degree of coupling between the power feeding coil and the power receiving coil to enable feeding efficiency to be enhanced. In such a feed system, communications by means of so-called load modulation are often performed prior to the power feeding to adjust the feed power, for example.
Incidentally, there are some wireless communications which switch operation modes depending on circumstances. For example, Patent Literature 1 discloses an RF tag which selects, depending on the status of power storage of a power storage section, a passive mode in which communications are performed by means of load modulation or an active mode in which communications are performed through operation by a power supplied by the power source storage section.